This invention relates to a carburetor vacuum shutoff control valve for reducing exhaust emissions and improving fuel economy of motor vehicles.
Atmospheric pollution, such as smog, is to a large extent formed by unburned or partially burned hydrocarbons in the exhaust gas emissions of motor vehicles. Incomplete combustion also reduces gasoline mileage.
Some of the worst exhaust gas emissions and fuel economy are produced when the vehicle decelerates, or "drifts", each time the driver takes his foot off the accelerator pedal. In engines having carbureted fuel systems, the throttle valve in the carburetor is closed when the vehicle decelerates, and the engine keeps running from the fuel being sucked into the intake manifold from the carburetor idle jets. During deceleration the pistons reciprocating in the cylinders create a sudden vacuum increase in the carburetor after the carburetor throttle valve closes. This vacuum increase sucks a rich fuel mixture into the intake manifold, which results in poor combustion which, in turn, increases exhaust gas emissions and reduces gasoline mileage during deceleration. Since normal city driving requires the driver to constantly take his foot off the accelerator pedal, the increased emissions and reduced gasoline mileage during deceleration are significant problems.
One solution to the smog problem has been the ignition timing device which retards the spark at idle speeds, but provides a spark advance during deceleration to allow as much time as possible for complete burning of the fuel in the combustion chambers. A typical approach has been to use a modified carburetor and distributor together with a vacuum-sensing control valve for varying the engine timing. The carburetor is specially calibrated to provide leaner fuel mixtures for idle and low speed operation. The distributor has a retarded ignition timing at idle speeds, and a vacuum advance control valve advances the ignition timing during deceleration. The valve relays a vacuum signal to the distributor during deceleration periods to advance the ignition timing and hopefully produce more complete combustion.
The present invention provides a carburetor vacuum-sensitive control valve which is an improvement over the conventional spark advance device because it is substantially more simple in construction and operation; and more importantly, it eliminates fuel being drawn into the combustion chambers during deceleration, which can lead to an overall improvement in gasoline mileage and lower exhaust gas and crankcase emissions.